In addition to the long and well-known type of camera which uses a photochemical process, there are also electronic cameras for taking still pictures which use an electronic, light-sensitive element. The most common type of light-sensitive element employs a charge-coupled device (CCD), which is includes a large number of CCD-elements, each of which constitutes a photosensor. By registering the level of illumination of each individual CCD-element, an image can be reproduced using the electrical information which is generated. This image may be presented on a display comprising, for example, a cathode ray tube (CRT) or liquid crystals (LCD). By filtering the incident light the image may also be decomposed into colors and its different color components may also be reproduced as a color image. In addition to presentation on a display, the electrical information may be reproduced as permanent images by some type of printer, and may also be transmitted or stored electronically.
In an electronic camera, image information is generated as an electrical signal and not, as in conventional cameras, as the result of a photochemical process. Electronic cameras thus offer certain advantages over the photochemical image production process. The image is for example generated immediately upon illumination of the photosensitive elements in the electronic camera and each change in the image may be registered. The image contents are immediately available for image analysis and for altering the image electronically, and the generated image signal can be transmitted immediately after it is created. On the other hand, there is the disadvantage that the image resolution is considerably worse than that which is achieved using good cameras having fine-grained film material. In applications requiring high resolution, a conventional camera is therefore irreplaceable.
In certain applications it may therefore be useful to combine a camera of the conventional type with an electronic camera to form a composite camera. In this way one may at each instant use the electronic camera to inspect the photographic subject which is located in front of the camera and even transmit this information for the purpose of remote control. When a picture is taken using the photochemical system the image content may simultaneously be registered electronically. Based on the electronically registered image, which can be both analyzed and transmitted electronically rapidly, one may then decide how the exposed film is to be processed: developed and printed either immediately or within a certain time period, or possibly not developed at all if the electronic image information indicates that the exposed film image will be of no interest or of unsatisfactory quality.
The possibility of obtaining an electronic image is also of great value in portrait photography. Since the photographic subject is constantly changing, the exposed picture may possibly not be acceptable. By examining the electronic image, one may thus avoid processing unusable pictures.
Composite cameras may also find use in space technology, whereby one could receive from space vehicles an instantaneous transmission of the contents of photochemically exposed pictures using the electronic camera. The photochemical image with its greater resolution may then be retrieved by a space shuttle, or after the space vehicle lands. The processing of the photochemical image is then determined on the basis of the information from the previously registered electronic image.
One way of producing a composite camera is to use the viewfinder system of a single-lens reflex (SLR) camera for recording the electronic image. This would, however, mean that the electronic image is available only up to a certain time before exposure of the photochemical image, that is, until the time when the mirror must be retracted and the lens stopped down. In systems with a human operator, one might often also wish to use the viewfinder system of the camera. In such systems it would be necessary to split the optical light beam, thereby reducing the light strength not only of the viewfinder image but also of the image projected on the CCD sensor unit.
The purpose of the present invention is to provide a composite camera for both photochemical and electronic image production which eliminates the above-mentioned disadvantages by allowing both camera systems to function separately, each according to its own technical specifications, and to automatically eliminate the problem of parallactic differences between the electronically registered image and the photochemically registered image.